The present invention pertains to a control system for continuously varying the speed of a fan drive motor for a forced air indoor space heating/cooling system during start-up and after shutdown of a heating/cooling cycle.
Forced air heating and cooling systems for indoor spaces in residential and commercial buildings are ubiquitous. A long-standing practice in controlling forced airflow through the heat exchanger, heating coils, evaporator coils and other heat exchange equipment in indoor space heating and cooling systems includes providing controls for the forced air fan or blower drive motor which delay startup of the drive motor when the heating or cooling source has been energized and another delay in shutdown of the fan drive motor after the heating/cooling system has been de-energized. Some conventional prior art controls do not provide for any delay of motor startup or shutdown. Conventional controls often provide for delayed startup of the fan drive motor at a single operating speed and delayed shutdown of the drive motor, again at a single maximum operating speed, after shutdown of the heating/cooling system in an effort to minimize unpleasant cold or hot drafts of air and to capture residual heat/cooling effect. However, controlling motor speed from being de-energized to full speed does not preclude stratification of air in the system ductwork or in the space being heated or cooled, nor does such operation maximize the capture of residual heat/cooling effect of the system heat exchange equipment.
Controls have also been developed for forced air heating/cooling systems wherein the indoor space air circulating fan drive motor is driven at reduced speed for a period of time during startup of the heating/cooling system and at a reduced speed for a period of time during the run-on or shutdown phase of the heating/cooling system operating cycle. Again, however, this type of control does not minimize the stratification of warm and cold air in the duct work or the space being heated or cooled nor does this type of system maximize the capture of residual heating/cooling effect.
Accordingly, there has been a strongly felt need for improvements in forced air circulation control in conventional heating and/or cooling systems including systems which use conventional electric motors, such as permanent split capacitor (PSC), shaded pole or other conventional electric motors used in a substantial number of heating/cooling systems manufactured for residential as well as commercial heating and cooling applications of indoor spaces. There has also been a strongly felt need for a fan or blower drive motor control system which may be easily retrofitted to a conventional heating/cooling system control circuits without modifying the circuits and without causing the controls for the heating/cooling system to be out of compliance with regulatory requirements. It is to these ends that the present invention has been developed.
The present invention provides an improved fan or blower drive motor control system and method for a forced air heating/cooling system for heating/cooling indoor spaces, in particular.
The present invention also provides an improved fan drive motor control system which is operable to substantially continuously vary the speed of the fan drive motor during a starting phase and a shutdown phase of operation of a conventional forced air heating/cooling system.
In particular, the invention comprises a control circuit which may be easily adapted to conventional heating/cooling system controls to vary the forced air fan or blower drive motor speed over predetermined time periods or which may be responsive to temperature sensed in the heating/cooling system airflow circuit.
In accordance with one important aspect of the invention, a control circuit is provided for a conventional AC electric motor drive mechanism for a forced air fan or blower which includes a timing circuit for operating the fan drive motor to continuously vary its speed from zero or a minimum start speed to a maximum or full speed operating speed condition during startup of the heating/cooling cycle, and for operating for a predetermined period of time while continuously reducing the fan speed cycle at the end of a heating/cooling operating cycle of the heating/cooling system. The control circuit includes a bias network, an on-board power supply, an AC voltage wave zero cross-over detector circuit and a control circuit for firing a triac to control the drive motor speed. The control system also includes a minimum speed detector circuit and a circuit which provides for continued operation of the motor at the minimum speed, if desired, or motor shutoff upon reaching the minimum speed.
In one embodiment of the control circuit or system of the invention, the system also senses temperature in the airflow circuit of the heating/cooling system and prevents premature or unwanted operation of the fan drive motor.
The control systems of the present invention advantageously reduce energy consumption of conventional forced air heating and cooling systems, improve recovery of residual heat/cooling effect in conventional forced air heating/cooling systems, minimize stratification of air in the airflow circuit and the space being heated or cooled and reduce cold or hot air drafts during operation of the heating/cooling system. Accordingly, the control systems of the present invention optimize the comfort level provided by a forced air heating/cooling system for an indoor space. Still further, by substantially continuously varying the fan or blower drive motor speed during a startup and shutdown phase, respectively, of an operating cycle, noise associated with fan or blower operation is reduced and the circulation of air at a temperature other than normally sensed or preferred by occupants of the indoor space is also reduced.